[PATCH v5] mm/vmalloc: lock contention optimization under multi-threading

rulinhuang
2024-02-23T13:01:13Z

When allocating a new memory area where the mapping address range is
known, it is observed that the vmap_area lock is acquired twice.
The first acquisition occurs in the alloc_vmap_area() function when
inserting the vm area into the vm mapping red-black tree. The second
acquisition occurs in the setup_vmalloc_vm() function when updating the
properties of the vm, such as flags and address, etc.
Combine these two operations together in alloc_vmap_area(), which
improves scalability when the vmap_area lock is contended. By doing so,
the need to acquire the lock twice can also be eliminated.
With the above change, tested on intel icelake platform(160 vcpu, kernel
v6.7), a 6% performance improvement and a 7% reduction in overall
spinlock hotspot are gained on
stress-ng/pthread(https://github.com/ColinIanKing/stress-ng), which is
the stress test of thread creations.

Reviewed-by: Chen Tim C <tim.c.chen@intel.com>
Reviewed-by: King Colin <colin.king@intel.com>
Signed-off-by: rulinhuang <rulin.huang@intel.com>
---
V1 -> V2: Avoided the partial initialization issue of vm and
separated insert_vmap_area() from alloc_vmap_area()
V2 -> V3: Rebased on 6.8-rc5
V3 -> V4: Rebased on mm-unstable branch
V4 -> V5: cancel the split of alloc_vmap_area()
and keep insert_vmap_area()
---
mm/vmalloc.c | 48 ++++++++++++++++++++++--------------------------
1 file changed, 22 insertions(+), 26 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 25a8df497255..6baaf08737f8 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1841,15 +1841,26 @@ node_alloc(unsigned long size, unsigned long align,
return va;
}

+static inline void setup_vmalloc_vm(struct vm_struct *vm,
+ struct vmap_area *va, unsigned long flags, const void *caller)
+{
+ vm->flags = flags;
+ vm->addr = (void *)va->va_start;
+ vm->size = va->va_end - va->va_start;
+ vm->caller = caller;
+ va->vm = vm;
+}
+
/*
* Allocate a region of KVA of the specified size and alignment, within the
- * vstart and vend.
+ * vstart and vend. If vm is passed in, the two will also be bound.
*/
static struct vmap_area *alloc_vmap_area(unsigned long size,
unsigned long align,
unsigned long vstart, unsigned long vend,
int node, gfp_t gfp_mask,
- unsigned long va_flags)
+ unsigned long va_flags, struct vm_struct *vm,
+ unsigned long flags, const void *caller)
{
struct vmap_node *vn;
struct vmap_area *va;
@@ -1912,6 +1923,9 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
va->vm = NULL;
va->flags = (va_flags | vn_id);

+ if (vm)
+ setup_vmalloc_vm(vm, va, flags, caller);
+
vn = addr_to_node(va->va_start);

spin_lock(&vn->busy.lock);
@@ -2486,7 +2500,8 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask)
va = alloc_vmap_area(VMAP_BLOCK_SIZE, VMAP_BLOCK_SIZE,
VMALLOC_START, VMALLOC_END,
node, gfp_mask,
- VMAP_RAM|VMAP_BLOCK);
+ VMAP_RAM|VMAP_BLOCK, NULL,
+ 0, NULL);
if (IS_ERR(va)) {
kfree(vb);
return ERR_CAST(va);
@@ -2843,7 +2858,8 @@ void *vm_map_ram(struct page **pages, unsigned int count, int node)
struct vmap_area *va;
va = alloc_vmap_area(size, PAGE_SIZE,
VMALLOC_START, VMALLOC_END,
- node, GFP_KERNEL, VMAP_RAM);
+ node, GFP_KERNEL, VMAP_RAM,
+ NULL, 0, NULL);
if (IS_ERR(va))
return NULL;

@@ -2946,26 +2962,6 @@ void __init vm_area_register_early(struct vm_struct *vm, size_t align)
kasan_populate_early_vm_area_shadow(vm->addr, vm->size);
}

-static inline void setup_vmalloc_vm_locked(struct vm_struct *vm,
- struct vmap_area *va, unsigned long flags, const void *caller)
-{
- vm->flags = flags;
- vm->addr = (void *)va->va_start;
- vm->size = va->va_end - va->va_start;
- vm->caller = caller;
- va->vm = vm;
-}
-
-static void setup_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va,
- unsigned long flags, const void *caller)
-{
- struct vmap_node *vn = addr_to_node(va->va_start);
-
- spin_lock(&vn->busy.lock);
- setup_vmalloc_vm_locked(vm, va, flags, caller);
- spin_unlock(&vn->busy.lock);
-}
-
static void clear_vm_uninitialized_flag(struct vm_struct *vm)
{
/*
@@ -3002,7 +2998,7 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
if (!(flags & VM_NO_GUARD))
size += PAGE_SIZE;

- va = alloc_vmap_area(size, align, start, end, node, gfp_mask, 0);
+ va = alloc_vmap_area(size, align, start, end, node, gfp_mask, 0, area, flags, caller);
if (IS_ERR(va)) {
kfree(area);
return NULL;
@@ -4584,7 +4580,7 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,

spin_lock(&vn->busy.lock);
insert_vmap_area(vas[area], &vn->busy.root, &vn->busy.head);
- setup_vmalloc_vm_locked(vms[area], vas[area], VM_ALLOC,
+ setup_vmalloc_vm(vms[area], vas[area], VM_ALLOC,
pcpu_get_vm_areas);
spin_unlock(&vn->busy.lock);
}

base-commit: c09a8e005eff6c064e2e9f11549966c36a724fbf
--
2.43.0